The mechanisms of action for the stimulation by insulins (natural and chemically-modified) and insulin-like growth factors were studied. The growth effect was measured by 3(H)-thymidine incorporation into cultured human fibroblasts; the metabolic effect was measured by stimulation of glucose oxidation in rat adipocytes. The relative order of potencies of different insulins diverges when metabolic effects and growth effects are compared. The divergences between two types of insulin action suggest that different domains on the insulin molecule are involved in the expression of these bioeffects.